Tumor progression, and particularly that of some neuroectodermal tumors (e.g., neuroblastoma and melanoma) causes most cancer-related morbidity and mortality. Thus, understanding and preventing progression is critical to developing effective cancer therapies. The synthesis and shedding of the membrane glycosphingolipids, gangliosides, has been strongly implicated by our past findings and the work of others in contributing to processes that facilitate tumor progression. Moreover, we have made significant progress in elucidating basic mechanisms in vitro by which gangliosides modulate the behavior of host cells found in the tumor microenvironment. We obtained clear evidence for the impact of ganglioside synthesis and shedding on cell signaling and on angiogenic responses of human endothelial cells, and found that pharmacological inhibition of glycosphingolipid synthesis has a striking inhibitory effect upon tumor growth. Based on these findings we hypothesize that gangliosides enhance tumor progression in vivo, and that interference with the synthesis of tumor gangliosides will impede tumor progression in vivo. However, an adequate animal model system of specific and constitutive inhibition of ganglioside synthesis in vivo has been lacking, and here we propose to fill this gap, by studying tumor progression in two different and complementary novel animal model systems that we are creating. In aim 1 we will develop two oncogene transformed ganglioside-deficient fibroblast tumor cell lines, one by GM3synthase/GM2synthase double knockout and the other by 4-OH-tamoxifen-inducible, cre-mediated deletion of glucosylceramide synthase (GCS). In aim 2 we will develop a unique ganglioside-depleted rodent tumor model by cre-mediated excision of the GCS gene in an orthotopic neuroectodermal (transgenic melanoma) tumor system in vivo. In Aim 3 we will comprehensively determine how ganglioside knockout in these ganglioside-depleted tumor systems affects tumor progression, providing the first unambiguous insights in vivo in a genetically controlled and stable system. Accomplishment of these aims will begin to elucidate the role and basic mechanisms by which gangliosides modulate tumor progression in vivo. This knowledge will lead to our ultimate goals of full delineation of the biological activity of tumor gangliosides in tumor progression and the development of novel therapeutic approaches to human cancer built upon this knowledge. PUBLIC HEALTH RELEVANCE: Understanding and prevention of tumor progression is critical for development of effective cancer therapies. The goal of the research proposed in this application is to determine exactly how production and shedding by tumor cells of a special type of lipids, named gangliosides, helps tumors to grow. The results of our studies will potentially allow modulation of ganglioside production/activity by tumors, which will in turn enable design of novel and effective treatments of cancer patients.